Sodium acetate

This article is about sodium acetate. For other uses of hot ice, see Hot ice (disambiguation).
Sodium acetate
Names
IUPAC name
Sodium acetate
Systematic IUPAC name
Sodium ethanoate
Other names
Hot ice (Sodium acetate trihydrate)
Identifiers
127‑09‑3 N
6131‑90‑4 (trihydrate) N
3D model (Jmol) Interactive image
ChEBI CHEBI:32954 YesY
ChEMBL ChEMBL1354 YesY
ChemSpider 29105 YesY
ECHA InfoCard 100.004.386
EC Number 204-823-8
E number E262 (preservatives)
PubChem 517045
RTECS number AJ4300010 (anhydrous)
AJ4580000
UNII NVG71ZZ7P0 YesY
Properties
C2H3NaO2
Molar mass 82.03 g·mol−1
Appearance White deliquescent powder
Odor Vinegar (acetic acid) odor when heated to decomposition[1]
Density 1.528 g/cm3 (20 °C, anhydrous)
1.45 g/cm3 (20 °C, trihydrate)[2]
Melting point 324 °C (615 °F; 597 K)
(anhydrous)
58 °C (136 °F; 331 K)
(trihydrate)
Boiling point 881.4 °C (1,618.5 °F; 1,154.5 K)
(anhydrous)
122 °C (252 °F; 395 K)
(trihydrate) decomposes
Anhydrous:
119 g/100 mL (0 °C)
123.3 g/100 mL (20 °C)
125.5 g/100 mL (30 °C)
137.2 g/100 mL (60 °C)
162.9 g/100 mL (100 °C)
Trihydrate:
32.9 g/100 mL (-10 °C)
36.2 g/100 mL (0 °C)
46.4 g/100 mL (20 °C)
82 g/100 mL (50 °C)[3]
Solubility Soluble in alcohol, hydrazine, SO2[4]
Solubility in methanol 16 g/100 g (15 °C)
16.55 g/100 g (67.7 °C)[4]
Solubility in ethanol Trihydrate:
5.3 g/100 mL
Solubility in acetone 0.5 g/kg (15 °C)[4]
Acidity (pKa) 24 (20 °C)[4]
4.76 CH3COOH[5]
Basicity (pKb) 9.25
1.464
Structure
Monoclinic
Thermochemistry
100.83 J/mol·K (anhydrous)[6]
229 J/mol·K (trihydrate)[7]
138.1 J/mol·K (anhydrous)[6]
262 J/mol·K (trihydrate)[2]
-709.32 kJ/mol (anhydrous)[4]
-1604 kJ/mol (trihydrate)[2]
-607.7 kJ/mol (anhydrous)[4]
Pharmacology
B05XA08 (WHO)
Hazards
Main hazards Irritant
Safety data sheet External MSDS
NFPA 704
Flammability code 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g., canola oil Health code 1: Exposure would cause irritation but only minor residual injury. E.g., turpentine Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
1
1
0
Flash point >250 °C (482 °F; 523 K) [5]
600 °C (1,112 °F; 873 K)[5]
Lethal dose or concentration (LD, LC):
3530 mg/kg (oral, rat)
Related compounds
Other anions
 Sodium formate
Sodium propionate
Other cations
 Potassium acetate
Calcium acetate
Related compounds
 Sodium diacetate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YesYN ?)
Infobox references

Sodium acetate, CH3COONa, also abbreviated NaOAc,[8] also known as sodium ethanoate, is the sodium salt of acetic acid. This colorless deliquescent salt has a wide range of uses.

Applications

Industrial

Sodium acetate is used in the textile industry to neutralize sulfuric acid waste streams and also as a photoresist while using aniline dyes. It is also a pickling agent in chrome tanning and helps to impede vulcanization of chloroprene in synthetic rubber production. In processing cotton for disposable cotton pads, sodium acetate is used to eliminate the buildup of static electricity.

Concrete longevity

Sodium acetate is used to mitigate water damage to concrete by acting as a concrete sealant, while also being environmentally benign and cheaper than the commonly used epoxy alternative for sealing concrete against water permeation.[9]

Food

Sodium acetate may be added to food as a seasoning, sometimes in the form of sodium diacetate, a one-to-one complex of sodium acetate and acetic acid,[10] given the E-number E262. It is often used to give potato chips a salt and vinegar flavor.

Buffer solution

As the conjugate base of acetic acid, a solution of sodium acetate and acetic acid can act as a buffer to keep a relatively constant pH level. This is useful especially in biochemical applications where reactions are pH-dependent in a mildly acidic range (pH 4-6).

Heating pad

A hand warmer containing a supersaturated solution of sodium acetate which releases heat upon crystallization

Sodium acetate is also used in heating pads, hand warmers, and hot ice. Sodium acetate trihydrate crystals melt at 136.4 °F/58 °C[11] (to 137.12 °F/58.4 °C),[12] dissolving in their water of crystallization. When they are heated past the melting point and subsequently allowed to cool, the aqueous solution becomes supersaturated. This solution is capable of cooling to room temperature without forming crystals. By pressing on a metal disc within the heating pad, a nucleation center is formed, causing the solution to crystallize back into solid sodium acetate trihydrate. The bond-forming process of crystallization is exothermic.[13][14] The latent heat of fusion is about 264–289 kJ/kg.[11] Unlike some types of heat packs, such as those dependent upon irreversible chemical reactions, a sodium acetate heat pack can be easily reused by immersing the pack in boiling water for a few minutes, until the crystals are completely dissolved, and allowing the pack to slowly cool to room temperature.[15]

Preparation

A crystal of sodium acetate trihydrate (length 1.7 centimetres)

For laboratory use, sodium acetate is inexpensive and usually purchased instead of being synthesized. It is sometimes produced in a laboratory experiment by the reaction of acetic acid, commonly in the 5–8% solution known as vinegar, with sodium carbonate ("washing soda"), sodium bicarbonate ("baking soda"), or sodium hydroxide ("lye"). Any of these reactions produce sodium acetate and water. When a sodium and carbonate ion-containing compound is used as the reactant, the carbonate anion from sodium bicarbonate or carbonate, reacts with hydrogen from the carboxyl group (-COOH) in acetic acid, forming carbonic acid. Carbonic acid readily decomposes under normal conditions into gaseous carbon dioxide and water. This is the reaction taking place in the well-known "volcano" that occurs when the household products, baking soda and vinegar, are combined.

CH3COOH + NaHCO3 → CH3COONa + H2CO
3
H2CO
3 → CO
2 + H
2O

Industrially, sodium acetate is prepared from glacial acetic acid and sodium hydroxide.

CH3COOH + NaOH → CH3COONa + H2O

Reactions

Sodium acetate can be used to form an ester with an alkyl halide such as bromoethane:

CH3COONa + BrCH2CH3 → CH3COOCH2CH3 + NaBr

Caesium salts catalyze this reaction.

References

  1. ↑ "Sodium Acetate". International Chemical Safety Cards. National Institute of Occupational Safety and Health.
  2. 1 2 3 http://chemister.ru/Database/properties-en.php?dbid=1&id=1510
  3. ↑ Seidell, Atherton; Linke, William F. (1952). Solubilities of Inorganic and Organic Compounds. Van Nostrand.
  4. 1 2 3 4 5 6 http://chemister.ru/Database/properties-en.php?dbid=1&id=172
  5. 1 2 3 Sigma-Aldrich Co., Sodium acetate. Retrieved on 2014-06-07.
  6. 1 2 Acetic acid, sodium salt in Linstrom, P.J.; Mallard, W.G. (eds.) NIST Chemistry WebBook, NIST Standard Reference Database Number 69. National Institute of Standards and Technology, Gaithersburg MD. http://webbook.nist.gov (retrieved 2014-05-25)
  7. ↑ Acetic acid, sodium salt, hydrate (1:1:3) in Linstrom, P.J.; Mallard, W.G. (eds.) NIST Chemistry WebBook, NIST Standard Reference Database Number 69. National Institute of Standards and Technology, Gaithersburg MD. http://webbook.nist.gov (retrieved 2014-05-25)
  8. ↑ Clayden, Jonathan; Greeves, Nick; Warren, Stuart; Wothers, Peter (2001). Organic Chemistry (1st ed.). Oxford University Press. ISBN 978-0-19-850346-0.
  9. ↑ "Potato Chip Flavoring Boosts Longevity Of Concrete". Science Daily. 8 August 2007.
  10. ↑ Jungbunzlauer - General Information
  11. 1 2 Ibrahim Dincer and Marc A. Rosen. Thermal Energy Storage: Systems and Applications, page 155
  12. ↑ [Courty JM, Kierlik E, Les chaufferettes chimiques, Pour la Science, décembre 2008, p 108-110]
  13. ↑ "Crystallization of Supersaturated Sodium Acetate". Journal of Chemical Education.
  14. ↑ Fake latent heat and supersaturation
  15. ↑ "How do sodium acetate heat pads work?". HowStuffWorks. Retrieved 2007-09-03.
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